Method and apparatus for controlling discontinuous reception in a wireless communication system

ABSTRACT

A method and apparatus for controlling Discontinuous Reception (DRX) by a User Equipment (UE) in a wireless communication system is provided. The UE receives a DRX configuration parameter from an evolved Node B (eNB), and determines whether to start an on-duration timer based on the DRX configuration parameter, after a change in DRX cycle is completed in a subframe, thereby preventing system performance degradation caused by transmission mismatch between the eNB and the UE.

PRIORITY

This application claims the benefit under 35 U.S.C. §119(a) of a Koreanpatent application filed in the Korean Intellectual Property Office onFeb. 16, 2010, and assigned Serial No. 10-2010-0013946, and a Koreanpatent application filed on May 3, 2010, and assigned Serial No.10-2010-0041609, the entire disclosures of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Discontinuous Reception (DRX) controlmethod and apparatus in a wireless communication system. Moreparticularly, the present invention relates to a DRX control method andapparatus capable of preventing system performance degradation caused bytransmission mismatch between an evolved Node B (eNB), also known as aBase Station (BS), and a User Equipment (UE), also known as a MobileStation (MS).

2. Description of the Related Art

Wireless communication systems have been developed to offercommunication services to users while ensuring user mobility. Due to therapid development of communication technologies, wireless communicationsystems can now provide not only voice communication services but alsohigh-speed data communication services. Recently, standardization for aLong Term Evolution (LTE) system, one of the next-generation wirelesscommunication systems, is underway in the 3rd Generation PartnershipProject (3GPP). The LTE system, scheduled to be commercialized in 2010,implements high-speed packet-based communication at a transfer rate of amaximum of 300 Mbps.

The 3GPP LTE system uses a DRX operation as one of the techniquessupported to reduce power consumption of a UE. In the LTE system, theDRX operation refers to an operation in which to reduce powerconsumption of a UE, the UE wakes up at a predetermined cycle to receivesystem information or paging messages transmitted from an eNB, and stopsits reception operation for the rest of the time. The DRX operation isdisclosed in the 3GPP Radio Access Network 2 (RAN2) standard TS 36.321,and it is provided that a DRX cycle is changed upon expiration of aspecific timer.

The DRX operation in the 3GPP LTE system is disclosed in detail inSection 5.7 of TS 36.321. In 3GPP, the state of a UE may be divided intoan idle state and a connected state according to the connection betweenthe UE and its eNB. The idle state is a state where the connection isreleased, while the connected state is a state where the connection isestablished. When the DRX operation is set in a Radio Resource Control(RRC) connected (RRC_CONNECTED) state, the UE discontinuously monitors aPhysical Downlink Control Channel (PDCCH), a control channel transmittedfrom the eNB, for reduction in transmission power. The discontinuousmonitoring for a control channel is carried out on a predetermined-cyclebasis. This cycle is called a DRX cycle. The DRX cycle is subject tochange according to the DRX operation.

FIG. 1 illustrates a DRX operation in an LTE system according to therelated art.

Referring to FIG. 1, a DRX cycle 101 includes an on-duration 103 inwhich a UE wakes up and monitors a PDCCH, or a control channel, and aDRX opportunity duration 105 in which the UE may stop the monitoringoperation. The UE periodically repeats the run/stop of the monitoringoperation according to the DRX cycle 101. The DRX cycle 101 refers to acycle during which the on-duration 103 is repeated, in which a UE wakesup and monitors a PDCCH, for example, a control channel. In the LTEsystem, a UE may receive a PDCCH, or a control channel transmitted by aneNB, in the on-duration 103, and the UE may operate in a sleep statewhere it does not monitor the PDCCH during the DRX opportunity duration105.

However, as for the DRX operation presently disclosed in the 3GPPstandard, no specific method defines how a UE should operate in asubframe where the DRX cycle changes. Due to this lack of a definedmethod in the LTE system, the DRX cycle applied may change according tothe determination time for start/non-start of an on-duration timer‘onDurationTimer’ that counts a time of the on-duration 103.

In addition, the DRX operation presently disclosed in the 3GPP TS 36.321standard is defined to determine whether to start the on-duration timer‘onDurationTimer’, without taking into account the possibility that theDRX cycle may change one or more times. This may lead to inconsistencybetween an eNB and a UE in DRX operation and cause malfunction of theon-duration timer ‘onDurationTimer’ due to the change in DRX cycle,resulting in system performance degradation due to the transmissionmismatch between the eNB and the UE.

SUMMARY OF THE INVENTION

An aspect of the present invention is to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide a DRX control method and apparatus that takes achange in DRX cycle into consideration in a wireless communicationsystem.

Another aspect of the present invention is to provide a method andapparatus for controlling a DRX operation-related timer taking a changein DRX cycle into account in a wireless communication system.

In accordance with one aspect of the present invention, a method forcontrolling Discontinuous Reception (DRX) by a User Equipment (UE) in awireless communication system is provided. The method includes receivinga DRX configuration parameter from an evolved Node B (eNB), and after achange in DRX cycle is completed in a subframe, determining whether tostart an on-duration timer based on the DRX configuration parameter.

In accordance with another aspect of the present invention, a UserEquipment (UE) for controlling Discontinuous Reception (DRX) in awireless communication system is provided. The UE includes a receiverfor receiving a DRX configuration parameter from an evolved Node B(eNB), and a controller for determining whether to start an on-durationtimer based on the DRX configuration parameter, after a change in DRXcycle is completed in a subframe.

In accordance with another aspect of the present invention, a method ofcontrolling DRX in a wireless communication system is provided. Themethod includes obtaining a DRX configuration parameter, and determiningwhether to start an on-duration timer based on the DRX configurationparameter.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certainexemplary embodiments of the present invention will be more apparentfrom the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a diagram illustrating a DRX operation in an LTE systemaccording to the related art;

FIG. 2 is a diagram illustrating protocol stacks on control planes of aUE and an eNB performing a DRX operation according to an exemplaryembodiment of the present invention;

FIGS. 3 to 8 are diagrams illustrating a DRX operation control methodaccording to exemplary embodiments of the present invention; and

FIG. 9 is a block diagram illustrating a structure of an apparatus forcontrolling a DRX operation according to an exemplary embodiment of thepresent invention.

Throughout the drawings, the same drawing reference numerals will beunderstood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding, but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art recognize that variouschanges and modifications of the embodiments described herein can bemade without departing from the scope and spirit of the invention. Inaddition, descriptions of well-known functions and constructions areomitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purposes only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

The below-described exemplary embodiments of the present inventionprovide various methods for controlling an operation of a DiscontinuousReception (DRX) operation-related timer taking a change in DRX cycleinto account. While exemplary embodiments of the present invention willbe described in connection with, for example, the Long Term Evolution(LTE) system, exemplary embodiments of the present invention may beapplied to any other wireless communication systems supporting the DRXoperation. In addition, while exemplary embodiments of the presentinvention will be described with reference to, for example, an operationof a User Equipment (UE), the present invention may be applied to anoperation of an evolved Node B (eNB).

FIG. 2 illustrates protocol stacks on control planes of a UE and an eNBperforming a DRX operation according to an exemplary embodiment of thepresent invention.

Referring to FIG. 2, RRC layers 210 and 310, MAC layers 230 and 330, andphysical (PHY) layers 250 and 350 take part in a DRX operation of thepresent invention in a UE 200 and an eNB 300, respectively. The DRXoperation is performed in downlink (DL) transmission from the eNB 300 tothe UE 200, and the below-described DRX operation in the DL transmissionmay be applied to uplink (UL) transmission as well.

The RRC layer 310 of the eNB 300 determines values of DRX configurationparameters to be transmitted to the UE 200, and delivers the determinedparameter values to the MAC layer 330. The DRX configuration parametersmay include expiration times of an on-duration timer ‘onDurationTimer’and a DRX inactivity timer ‘drx-InactivityTimer’. The on-duration timer‘onDurationTimer’ and the DRX inactivity timer ‘drx-InactivityTimer’count the times when the UE 200 may stop monitoring a control channeland enter a sleep state. The on-duration timer ‘onDurationTimer’ is atimer indicating the time during which the UE 200 continuously monitorsa control channel in every DRX cycle. The DRX inactivity timer‘drx-InactivityTimer’ is a timer indicating a predetermined time duringwhich the UE 200 is awakened continuously after the transmission orreception when a new packet is transmitted from or received at the eNB300.

In addition, the DRX configuration parameters may include at least oneparameter indicating a long DRX cycle ‘longDRX-Cycle’, a DRX startoffset ‘drxStartOffset’, an expire time of a short DRX cycle timer‘drxShortCycleTimer’, and a short DRX cycle ‘shortDRX-Cycle’. The UE 200determines an application time of the on-duration timer‘onDurationTimer’, defining the long DRX cycle ‘longDRX-Cycle’ receivedfrom the eNB 300 as a basic DRX cycle. However, if the short DRX cycle‘shortDRX-Cycle’ is set as available, the UE 200 may determine anapplication time of the on-duration timer ‘onDurationTimer’ by applyingthe short DRX cycle ‘shortDRX-Cycle’ beginning from the time where theDRX inactivity timer ‘drx-InactivityTimer’ expires. This short DRX cycle‘shortDRX-Cycle’ is applied until the short DRX cycle timer‘drxShortCycleTimer’ expires. The DRX start offset ‘drxStartOffset’denotes an offset for a start time of the on-duration timer‘onDurationTimer’.

The DRX cycle may be set differently according to the frequency of datatransmission/reception. For example, when the UE 200 downloads a webpage during web browsing, the UE 200 may use a short DRX cycle becauseof the frequent data transmission/reception, and may use the short DRXcycle ‘shortDRX-Cycle’ according to a specific rule. On the other hand,when a user reads a web page, the UE 200 may use a long DRX cyclebecause of the infrequent data transmission/reception, and may use thelong DRX cycle ‘longDRX-Cycle’ according to a specific rule.

The MAC layer 330 of the eNB 300 sends the DRX configuration parametersto the PHY layer 350 using a delivery channel. The PHY layer 350transmits the DRX configuration parameters to the PHY layer 250 of theUE 200 through a PHY channel 201. The RRC layer 210 of the UE 200analyzes the DRX configuration parameters received from the PHY layer250 and delivers the analyzed parameters to the MAC layer 230, so thatthe DRX operation according to an exemplary embodiment of the presentinvention, in which a change in the DRX cycle is taken intoconsideration, is performed in each of the UE 200 and the eNB 300.Setting of DRX-related parameters is performed in the RRC layers 210 and310 of the UE 200 and the eNB 300. The overall operation of controllingthe DRX operation using the set DRX-related parameters is performed inthe MAC layers 230 and 330 of the UE 200 and the eNB 300. A DRXoperation control method according to exemplary embodiments of thepresent invention is described in detail below.

The MAC layer 230 controls a DRX operation using the DRX configurationparameters received from the eNB 300. These parameters include at leastone of the expiration times of the on-duration timer ‘onDurationTimer’and the DRX inactivity timer ‘drx-InactivityTimer’, the long DRX cycle‘longDRX-Cycle’, the DRX start offset ‘drxStartOffset’, the expirationtime of the short DRX cycle timer ‘drxShortCycleTimer’, and the shortDRX cycle ‘shortDRX-Cycle’. While the on-duration timer‘onDurationTimer’ and the DRX inactivity timer ‘drx-InactivityTimer’ arerunning, the UE 200 monitors a PDCCH, and when set to use the DRXoperation, the UE 200 performs one of the following operations in eachsubframe:

-   -   The UE 200 starts the on-duration timer ‘onDurationTimer’, if        the short DRX cycle ‘shortDRX-Cycle’ is used and the remainder        obtained by dividing [(SFN*10)+subframe number] by the short DRX        cycle ‘shortDRX-Cycle’ is equal to the remainder obtained by        dividing the DRX start offset ‘drxStartOffset’ by the short DRX        cycle ‘shortDRX-Cycle’.    -   The UE 200 starts the on-duration timer ‘onDurationTimer’, if        the long DRX cycle ‘longDRX-Cycle’ is used and the remainder        obtained by dividing [(SFN*10)+subframe number] by the long DRX        cycle ‘longDRX-Cycle’ is equal to the DRX start offset        ‘drxStartOffset’.    -   The UE 200 starts the short DRX cycle timer ‘drxShortCycleTimer’        and sets the short DRX cycle ‘shortDRX-Cycle’ and uses the        ‘shortDRX-Cycle’, if the DRX inactivity timer        ‘drx-InactivityTimer’ expires in this subframe, or a DRX command        MAC control element indicating a change in the DRX cycle is        received from the eNB 300 and the short DRX cycle ‘        shortDRX-Cycle’ is set in this subframe.    -   The UE 200 sets the long DRX cycle ‘longDRX-Cycle’ and uses the        ‘longDRX-Cycle’, if the DRX inactivity timer        ‘drx-InactivityTimer’ expires in this subframe, or a DRX command        MAC control element indicating a change in the DRX cycle is        received from the eNB 300 and the short DRX cycle        ‘shortDRX-Cycle’ is not set in this subframe.    -   The UE 200 sets the long DRX cycle ‘longDRX-Cycle’ and uses the        ‘longDRX-Cycle’, if the short DRX cycle timer        ‘drxShortCycleTimer’ expires in this subframe.

In the foregoing description of the DRX operation, SFN denotes a systemframe number.

In accordance with the DRX operation control method described above, theDRX cycle changes if the DRX inactivity timer ‘drx-InactivityTimer’expires, a DRX command MAC control element is received, or the short DRXcycle timer ‘drxShortCycleTimer’ expires in this subframe.

Exemplary embodiments of the present invention propose the following DRXoperation methods for the case where the DRX cycle is changed or to bechanged one or more times. The following embodiments provide varioustypes of DRX operation control methods for determining whether to starta DRX operation-related timer after checking at least one condition thata change in the DRX cycle occurs, or for checking at least one conditionin which a change in DRX cycle occurs, after determining whether tostart a DRX operation-related timer.

In embodiment 1, whether to start an on-duration timer ‘onDurationTimer’is determined before a DRX cycle is changed in a relevant subframe.

In embodiment 2, whether to start an on-duration timer ‘onDurationTimer’is determined after a DRX cycle is changed n times in a relevantsubframe.

In embodiment 3, whether to start an on-duration timer ‘onDurationTimer’is determined after a change in DRX cycle is fully completed in arelevant subframe.

In embodiment 4, whether to start an on-duration timer is determinedbefore or after checking a specific condition in a relevant subframe.

In embodiment 5 a DRX inactivity timer ‘drx-InactivityTimer’ isconsidered to expire first, if both of the DRX inactivity timer ‘drx-InactivityTimer’ and the short DRX cycle timer ‘drxShortCycleTimer’are to expire in a relevant subframe.

In embodiment 6 the current DRX cycle is maintained so as to prevent achange in DRX cycle from occurring within a short period when the shortDRX cycle timer ‘drxShortCycleTimer’ restarts after its expiration in animpending subframe.

Embodiments 1 to 6 will be described in more detail with reference toFIGS. 3 to 8.

Embodiment 1

FIG. 3 illustrates a DRX operation control method according to anexemplary embodiment of the present invention.

Referring to FIG. 3, in each subframe the UE determines whether to startan on-duration timer ‘onDurationTimer’ before checking a condition wherea change in DRX cycle occurs. In Embodiment 1, because the change in DRXcycle occurs (i) when the DRX inactivity timer ‘drx-InactivityTimer’expires in this subframe, (ii) when the DRX command MAC control elementis received from an eNB in this subframe, and (iii) when the short DRXcycle timer ‘drxShortCycleTimer’ expires in this subframe, the UEdetermines whether to start the on-duration timer ‘onDurationTimer’before checking these three conditions (301). FIG. 3 illustrates a DRXoperation for the case (303) in which the short DRX cycle timer ‘drxShortCycleTimer’ expires.

Embodiment 2

FIG. 4 illustrates a DRX operation control method according to anexemplary embodiment of the present invention.

Referring to FIG. 4, a UE determines whether to start an on-durationtimer ‘onDurationTimer’ after a DRX cycle changes n times in a subframe.Because the change in DRX cycle occurs (i) when the DRX inactivity timer‘drx-InactivityTimer’ expires in this subframe, (ii) when the DRXcommand MAC control element is received from an eNB in this subframe,and (iii) when the short DRX cycle timer ‘drxShortCycleTimer’ expires inthis subframe, the UE determines whether to start the on-duration timer‘onDurationTimer’ if the DRX cycle changes n times during or after theconditions are checked. FIG. 4 illustrates an example of determiningwhether to start the on-duration timer ‘onDurationTimer’ (403) after theDRX cycle is changed once due to expiration of the short DRX cycle timer‘ drxShortCycleTimer’ (401).

Embodiment 3

FIG. 5 illustrates a DRX operation control method according to anexemplary embodiment of the present invention.

Referring to FIG. 5, the UE determines whether to start an on-durationtimer ‘onDurationTimer’ after a change in DRX cycle is fully completedin a subframe. Because the change in DRX cycle occurs (i) when the DRXinactivity timer ‘drx-InactivityTimer’ expires in this subframe, (ii)when the DRX command MAC control element is received from an eNB in thissubframe, and (iii) when the short DRX cycle timer ‘drxShortCycleTimer’expires in this subframe, the UE determines whether to start theon-duration timer ‘onDurationTimer’ after all of the conditions arechecked. The exemplary embodiment of FIG. 5 represents an example wherethe UE determines whether to start the on-duration timer‘onDurationTimer’ (505), after both of the two conditions are checked(501 and 503).

FIG. 6 illustrates a DRX operation control method according to anexemplary embodiment of the present invention.

Referring to FIG. 6, the UE recognizes DRX configuration parameters instep 605. For the parameter recognition, an eNB may notify the DRXconfiguration parameters to the UE in a call setup process or the like.The DRX configuration parameters may include, for example, expirationtimes of an on-duration timer ‘onDurationTimer’ and a DRX inactivitytimer ‘drx-InactivityTimer’, a long DRX cycle ‘longDRX-Cycle’, a DRXstart offset ‘drxStartOffset’, an expiration time of a short DRX cycletimer ‘drxShortCycleTimer’, and a short DRX cycle ‘shortDRX-Cycle’.

The UE performs a DRX operation from the time that it recognizes the DRXconfiguration parameters. Performing a DRX operation includesdetermining whether to start a specific timer described in detail inSection 5.7 of TS 36.321, in each subframe, and performing a specificoperation, for example, PDCCH monitoring, according to the start of thetimer.

While performing the DRX operation, the UE determines a change/no-changein DRX cycle in each subframe in step 610. Just before a specificsubframe starts in which a change/no-change in DRX cycle is to bedetermined, the UE determines whether the short DRX cycle timer‘drxShortCycleTimer’ or the DRX inactivity timer ‘drx-InactivityTimer’is scheduled to expire in the subframe. If the short DRX cycle timer‘drxShortCycleTimer’ is scheduled to expire, the UE determines that theDRX cycle will change from the short DRX cycle ‘shortDRX-Cycle’ to thelong DRX cycle ‘longDRX-Cycle’ in the subframe. If the DRX inactivitytimer ‘drx-InactivityTimer’ is scheduled to expire in the subframe, or aDRX command MAC control element is received from an eNB and a DRX cycleat this time is the long DRX cycle ‘longDRX-Cycle’ in the subframe, thenthe UE determines that the DRX cycle will change from the long DRX cycle‘longDRX-Cycle’ to the short DRX cycle ‘shortDRX-Cycle’ in the subframe.

If there is no change in the DRX cycle in step 610, the UE determineswhether to start the on-duration timer ‘onDurationTimer’ in the subframeusing the current DRX cycle in step 615.

If there is a change in the DRX cycle in step 610, the UE proceeds tostep 620. Except for the case where a DRX command MAC control element isreceived, the change in DRX cycle in an arbitrary subframe indicatesexpiration of the DRX inactivity timer ‘drx-InactivityTimer’, expirationof the short DRX cycle timer ‘drxShortCycleTimer’, or expiration of bothtimers in the subframe. If only one of the two timers expires, whichmeans that the DRX cycle changes only once, the UE determines whether tostart the on-duration timer ‘onDurationTimer’ in the subframe using thechanged DRX cycle after the change in the DRX cycle.

If the changed DRX cycle is the short DRX cycle ‘shortDRX-Cycle’, the UEcompares the remainder obtained by dividing [(SFN*10)+subframe number]by the short DRX cycle ‘shortDRX-Cycle’ with the remainder obtained bydividing the DRX start offset ‘drxStartOffset’ by the short DRX cycle‘shortDRX-Cycle’. The UE determines whether to start the on-durationtimer ‘onDurationTimer’ depending on whether the remainders areidentical to each other.

If the changed DRX cycle is the long DRX cycle ‘longDRX-Cycle’, the UEcompares the remainder obtained by dividing [(SFN*10)+subframe number]by the long DRX cycle ‘longDRX-Cycle’ with the DRX start offset‘drxStartOffset’. The UE determines whether to start the on-durationtimer ‘onDurationTimer’ based on the comparison.

If both of the DRX inactivity timer ‘drx-InactivityTimer’ and the shortDRX cycle timer ‘drxShortCycleTimer’ expire in the same subframe, theDRX cycle changes twice in the subframe. In this case, the UE determineswhether to start the on-duration timer ‘onDurationTimer’ in the subframeusing the final DRX cycle after the DRX cycle is fully changed. In step620, the UE determines whether to start the on-duration timer‘onDurationTimer’ after the DRX cycle is completely changed in anarbitrary subframe. Otherwise, in determining whether to start theon-duration timer ‘onDurationTimer’ in an arbitrary subframe, the UEdetermines whether to start the on-duration timer ‘onDurationTimer’using the final DRX cycle of the subframe.

If both of the DRX inactivity timer ‘drx-InactivityTimer’ and the shortDRX cycle timer ‘drxShortCycleTimer’ expire in the same subframe, theDRX cycle may either change or not change in the subframe according towhich timer expires first. For example, if the short DRX cycle timer‘drxShortCycleTimer’ expires before the DRX inactivity timer‘drx-InactivityTimer’, the DRX cycle changes from the short DRX cycle‘shortDRX-Cycle’ to the long DRX cycle ‘longDRX-Cycle’ and then changesback to the short DRX cycle ‘shortDRX-Cycle’.

On the other hand, if the DRX inactivity timer ‘drx-InactivityTimer’expires first, then the DRX cycle is maintained as the short DRX cycle‘shortDRX-Cycle’ without changing, because the expiration of the DRXinactivity timer ‘drx-InactivityTimer’ triggers a restart of the shortDRX cycle timer ‘drxShortCycleTimer’.

In both of the two cases, their final DRX cycles are equal to the shortDRX cycle ‘shortDRX-Cycle’. Rather than changing the DRX cycle severaltimes in one subframe, the DRX cycle should not be changed, so as toreduce a processing load of the UE. In Embodiment 5 of the presentinvention, if the two timers are both scheduled to expire in anarbitrary subframe, the UE is set to consider that the DRX inactivitytimer ‘drx-InactivityTimer’ has expired first, thereby preventingunnecessary changes in the DRX cycle.

Embodiment 4

In Embodiment 4, the UE determines whether to start an on-duration timer‘onDurationTimer’ before or after checking a specific cycle changecondition in every subframe. Because the change in DRX cycle occurs (i)when the DRX inactivity timer ‘drx-InactivityTimer’ expires in thissubframe, (ii) when the DRX command MAC control element is received froman eNB in this subframe, and (iii) when the short DRX cycle timer‘drxShortCycleTimer’ expires in this subframe, the UE determines whetherto start the on-duration timer ‘onDurationTimer’ before/after checkingone or more conditions.

Embodiment 5

FIG. 7 illustrates a DRX operation control method according to anexemplary embodiment of the present invention.

Referring to FIG. 7, a UE recognizes DRX configuration parameters instep 705. For the parameter recognition, an eNB may notify the DRXconfiguration parameters to the UE in a call setup process or the like.The DRX configuration parameters may include, for example, expirationtimes of an on-duration timer ‘onDurationTimer’ and a DRX inactivitytimer ‘drx-InactivityTimer’, a long DRX cycle ‘longDRX-Cycle’, a DRXstart offset ‘drxStartOffset’, an expiration time of a short DRX cycletimer ‘drxShortCycleTimer’, and a short DRX cycle ‘shortDRX-Cycle’.

In step 710, the UE determines whether both of the DRX inactivity timer‘drx-InactivityTimer’ and the short DRX cycle timer ‘drxShortCycleTimer’are scheduled to expire in an impending subframe. The impending subframemay be, for example, the next subframe.

If the two timers are not both scheduled to expire, the UE operatesaccording to the related art in step 720. On the other hand, if the twotimers are both scheduled to expire in the same subframe, the UEconsiders in step 715 that the DRX inactivity timer‘drx-InactivityTimer’ expires first in the impending subframe, andperforms a related operation. The UE first performs a specific operationassociated with the expiration of the DRX inactivity timer‘drx-InactivityTimer’ before performing a specific operation associatedwith the expiration of the short DRX cycle timer ‘drxShortCycleTimer’.

The specific operation associated with the expiration of the short DRXcycle timer ‘drxShortCycleTimer’ may be, for example, a change from theshort DRX cycle ‘shortDRX-Cycle’ to the long DRX cycle ‘longDRX-Cycle’.The specific operation associated with the expiration of the DRXinactivity timer ‘drx-InactivityTimer’ may be a restart of the short DRXcycle timer ‘drxShortCycleTimer’. As a result, as the short DRX cycletimer ‘drxShortCycleTimer’ restarts, the short DRX cycle timer‘drxShortCycleTimer’ does not expire in the subframe, preventingunnecessary changes in the DRX cycle.

In a further normalization of Embodiment 5, if a plurality of timersincluding the DRX inactivity timer ‘drx-InactivityTimer’ are scheduledto expire in an arbitrary subframe, the UE may first perform a specificoperation associated with the expiration of the DRX inactivity timer‘drx-InactivityTimer’, considering that the DRX inactivity timer‘drx-InactivityTimer’ expires first. If the DRX operation controlmethods according to the above exemplary embodiments are applied, amismatch in active time due to the change in DRX cycle may be preventedfor both the UE and the eNB, and the UE may prevent system performancedegradation caused by the transmission mismatch with the eNB, whilemaintaining the power consumption reduction effects by the DRXoperation.

Embodiment 6

Referring to v9.2.0 in the 3GPP standard TS 36.321, a UE starts applyinga long DRX cycle in a subframe where a short DRX cycle timer‘drxShortCycleTimer’ expires. However, in the case where a DRXinactivity timer ‘drx-InactivityTimer’ expires in the same subframewhere the short DRX cycle timer ‘drxShortCycleTimer’ expires, dependingon the implementation method, the UE may operate in such a manner thatit uses the short DRX cycle ‘shortDRX-Cycle’ in the previous subframe,applies the long DRX cycle ‘longDRX-Cycle’ in the current subframe, andapplies the short DRX cycle ‘shortDRX-Cycle’ again in the next subframe.For example, upon expiration of the above timers, the UE may, in order,check expiration of the short DRX cycle timer ‘ drxShortCycleTimer’,determine whether to start the on-duration timer ‘onDurationTimer’, andcheck expiration of the DRX inactivity timer ‘drx-InactivityTimer’. Inthis case, the UE may use the short DRX cycle ‘shortDRX-Cycle’ caused byrunning the short DRX cycle timer ‘drxShortCycleTimer’ in the previoussubframe, apply the long DRX cycle ‘longDRX-Cycle’ caused by theexpiration of the short DRX cycle timer ‘drxShortCycleTimer’ in thecurrent subframe, and apply the short DRX cycle ‘shortDRX-Cycle’ againdue to the expiration of the DRX inactivity timer ‘drx-InactivityTimer’in the next subframe. However, transitioning from the short DRX cycle tothe long DRX cycle and back from the long DRX cycle to the short DRXcycle within this short period increases the complexity of the UE andhas no real benefit.

Embodiment 6 of the present invention provides a method for preventing aUE from changing a long DRX cycle in the above situation.

FIG. 8 illustrates a DRX operation control method according to anexemplary embodiment of the present invention.

Referring to FIG. 8, a UE recognizes DRX configuration parameters instep 805. For the parameter recognition, an eNB may notify the DRXconfiguration parameters to the UE in a call setup process or the like.The DRX configuration parameters may include, for example, expirationtimes of an on-duration timer ‘onDurationTimer’ and a DRX inactivitytimer ‘drx-InactivityTimer’, a long DRX cycle ‘longDRX-Cycle’, a DRXstart offset ‘drxStartOffset’, an expiration time of a short DRX cycletimer ‘drxShortCycleTimer’, and a short DRX cycle ‘shortDRX-Cycle’.

In step 810, the UE determines whether the short DRX cycle timer‘drxShortCycleTimer’ is scheduled to expire in an impending subframe.The impending subframe may be, for example, the next subframe.

If the short DRX cycle timer ‘drxShortCycleTimer’ is not scheduled toexpire in step 810, the UE maintains the DRX cycle currently in use instep 820. If the short DRX cycle timer ‘drxShortCycleTimer’ is scheduledto expire in step 810, the UE determines in step 815 whether the shortDRX cycle timer ‘drxShortCycleTimer’ restarts after its expiration inthe impending subframe. Because the short DRX cycle timer's notrestarting after its expiration in the impending subframe indicates thatthe short DRX cycle timer ‘drxShortCycleTimer’ is not running in theimpending state, step 815 may be modified for the UE to determinewhether the short DRX cycle timer ‘drxShortCycleTimer’ is running in theimpending subframe. If the short DRX cycle timer ‘drxShortCycleTimer’restarts (or the short DRX cycle timer ‘drxShortCycleTimer’ a running)after its expiration in the impending subframe in step 815, the UEmaintains the short DRX cycle ‘shortDRX-Cycle’ now in use in step 820 sothat the DRX cycle does not transition to the long DRX cycle‘longDRX-Cycle’. If the short DRX cycle timer ‘drxShortCycleTimer’ doesnot restart (or the short DRX cycle timer ‘drxShortCycleTimer’ is not ina running state) after its expiration in the impending subframe in step815, the UE applies the long DRX cycle ‘longDRX-Cycle’ in step 825.

Accordingly, application of above-described Embodiment 6 may preventunnecessary DRX transition from occurring within a short period.

FIG. 9 conceptually illustrates a structure of an apparatus forcontrolling a DRX operation according to an exemplary embodiment of thepresent invention. The DRX operation control apparatus of FIG. 9 isincluded in a UE communicating with an eNB.

Referring to FIG. 9, a receiver 903 receives the DRX configurationparameters transmitted from an eNB (not shown), under control of acontroller 905. The DRX configuration parameters received through anantenna 901 and the receiver 903 are delivered to the controller 905.The controller 905 determines whether to start a DRX operation-relatedtimer using the DRX configuration parameters in each subframe beforechecking at least one condition in which a change in DRX cycle occurs.The controller 905 may make the determination according to one of theexemplary embodiments described above. For example, when a DRX operationis set in an RRC connected state, the controller 905 may control the DRXoperation according to the determination results and discontinuouslymonitor a control channel or the like transmitted from the eNB. Whenusing above-described Embodiment 6, the controller 905 may determinewhether a short DRX cycle timer restarts in an impending subframe usingthe DRX configuration parameters, after the short DRX cycle timerexpires in the impending subframe, and if the short DRX cycle timerrestarts, the controller 905 may maintain the current DRX cycle, therebypreventing unnecessary DRX transition from occurring within a shortperiod. The controller 905 controls the DRX operation according toexemplary embodiments of the present invention in its RRC layer.

While the invention has been shown and described with reference tocertain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for controlling Discontinuous Reception(DRX) by a User Equipment (UE) in a wireless communication system, themethod comprising: receiving a DRX configuration from an evolved Node B(eNB); and after a DRX cycle is changed from a short DRX cycle to a longDRX cycle in a subframe or a DRX cycle is changed from a long DRX cycleto a short DRX cycle in a subframe, determining whether to start anon-duration timer based on the DRX configuration.
 2. The method of claim1, wherein the on-duration timer indicates a time for which the UEmonitors a control channel in each DRX cycle.
 3. The method of claim 1,wherein the the DRX cycle is changed in the subframe when a DRXinactivity timer and a short DRX cycle timer both expire in thesubframe.
 4. The method of claim 3, wherein the DRX inactivity timer isconsidered to expire before the short DRX cycle timer.
 5. The method ofclaim 1, wherein the DRX configuration comprises at least one of anexpiration time of an on-duration timer ‘onDurationTimer’, an expirationtime of a DRX inactivity timer ‘drx-InactivityTimer’, the long DRX cycle‘longDRX-Cycle’, a DRX start offset ‘drxStartOffset’, an expiration timeof a short DRX cycle timer ‘drxShortCycleTimer’, and the short DRX cycle‘shortDRX-Cycle’.
 6. The method of claim 1, wherein the determining ofwhether to start an on-duration timer comprises starting an on-durationtimer ‘onDurationTimer’, if the short DRX cycle ‘shortDRX-Cycle’ is usedand a remainder obtained by dividing [(System Frame Number(SFN)*10)+subframe number] by the short DRX cycle ‘shortDRX-Cycle’ isequal to a remainder obtained by dividing a DRX start offset‘drxStartOffset’ by the short DRX cycle ‘shortDRX-Cycle’.
 7. The methodof claim 1, wherein the determining of whether to start an on-durationtimer comprises starting an on-duration timer ‘onDurationTimer’, if thelong DRX cycle ‘longDRX-Cycle’ is used and a remainder obtained bydividing [(SFN*10)+subframe number] by the long DRX cycle‘longDRX-Cycle’ is equal to a DRX start offset ‘drxStartOffset’.
 8. Themethod of claim 4, further comprising: restarting the short DRX cycletimer according to expiration of the short DRX cycle timer in thesubframe.
 9. The method of claim 1, wherein the determining of whetherto start the on-duration timer comprises: determining whether to startthe on-duration timer after a predetermined number of DRX cycle changesoccur in a current subframe.
 10. The method of claim 1, wherein thedetermining of whether to start the on-duration timer comprises:determining whether to start the on-duration timer after the DRX cyclefully changes.
 11. The method of claim 1, further comprising:maintaining a current DRX cycle when the short DRX cycle is scheduled toexpire and restart in a subframe following a current subframe.
 12. AUser Equipment (UE) for controlling Discontinuous Reception (DRX) in awireless communication system, the UE comprising: a receiver forreceiving a DRX configuration from an evolved Node B (eNB); and acontroller for determining whether to start an on-duration timer basedon the DRX configuration, after a DRX cycle is changed from a short DRXcycle to a long DRX cycle in a subframe or a DRX cycle is changed from along DRX cycle to a short DRX cycle in a subframe.
 13. The UE of claim12, wherein the on-duration timer indicates a time for which the UEmonitors a control channel in each DRX cycle.
 14. The UE of claim 12,wherein the controller determines that the DRX cycle is changed in thesubframe when a DRX inactivity timer and a short DRX cycle timer bothexpire in the subframe.
 15. The UE of claim 14, wherein the controllerconsiders the DRX inactivity timer to expire before the short DRX cycletimer.
 16. The UE of claim 12, wherein the DRX configuration comprisesat least one of an expiration time of an on-duration timer‘onDurationTimer’, an expire time of a DRX inactivity timer‘drx-InactivityTimer’, the long DRX cycle ‘longDRX-Cycle’, a DRX startoffset ‘drxStartOffset’, an expiration time of a short DRX cycle timer‘drxShortCycleTimer’, and the short DRX cycle ‘shortDRX-Cycle’.
 17. TheUE of claim 12, wherein the controller determines to start theon-duration timer ‘onDurationTimer’, if the short DRX cycle‘shortDRX-Cycle’ is used and a remainder obtained by dividing [(SystemFrame Number (SFN)*10)+subframe number] by the short DRX cycle‘shortDRX-Cycle’ is equal to a remainder obtained by dividing a DRXstart offset ‘drxStartOffset’ by the short DRX cycle ‘shortDRX-Cycle’.18. The UE of claim 12, wherein the controller determines to start theon-duration timer ‘onDurationTimer’, if the long DRX cycle‘longDRX-Cycle’ is used and a remainder obtained by dividing[(SFN*10)+subframe number] by the long DRX cycle ‘longDRX-Cycle’ isequal to a DRX start offset ‘drxStartOffset’.
 19. The UE of claim 15,wherein the controller further controls to restart the short DRX cycletimer according to expiration of the short DRX cycle timer in thesubframe.